High speed catadioptric objective lens system

ABSTRACT

This invention provides a high speed compact catadioptric, i.e. reflecting-refracting objective system of F/1.2. 
     The lens system comprises, in accordance with the advance of the light rays, a positive lens with a convex surface toward the object, a lens with front and back surface concave toward the object and with a main mirror surfaced on the peripheral portion of said back surface. A counter-mirror is surfaced to the central portion of said positive lens and a field lens is cemented to the central portion of said lens with the main mirror surfaced thereon. Small zonal errors of spherical aberration, economical production and a reduced sensitivity to machining and mounting errors result from employing only two optical members which carry the mirrors and lens elements.

This is a continuation, of application Ser. No. 967,973 filed Dec. 8, 1978, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improved reflecting-refracting high speed objective lens in which all optical elements are assembled in two members.

2. Description of the Prior Art

The reflecting objective lens, as initially used in astronomy, is distinguished by its ideally achromatic image which is exceptionally useful with large focal lengths. A further advantage over refracting lenses is given by the reduced length which enhanced the use of reflecting telephoto lenses in photography.

Recently reflecting lenses have proven very useful for electronic infrared- and night-vision systems featuring high speed--high contrast objectives with reduced image angle. Reflecting-refracting or catadioptric lenses were designed in order to use only spherical mirrors, to extend the field of view and to reduce image errors by introducing ordinary refracting lenses for correction purposes. The thus created Maksutov-lens nevertheless exhibits a large zonal error of spherical aberration.

Another similar type, the Mandler-lens, having a two member front part (it likewise presents a large zonal error of spheric aberration) is disclosed e.g. in F. I. Havlicek, L. Canzek "Zum Korrigieren von Spiegelobjektiven", Deutsche Geodatische Kommission bei der Bayerischen Akademie der Wissenschaften, Reihe A, Heft 42, Munchen 1963.

A further improvement was brought about by using a one member front lens, the silvered central part of which constitutes the second mirror, while the first or main mirror has a central bore as disclosed by Swiss Pat. No. 542,454. These known objective lenses nevertheless suffer from at least one of the following short-comings:

(a) A central bore is applied to the main mirror involving a high cost, machining of a ring-shaped lens is difficult, and such a lens has a reduced mechanical stability as compared to a solid lens.

(b) The front lens, the main mirror and the field lens system are rather sensitive to centering. Without exact centering troublesome comatic and astigmatic defects are unavoidable.

(c) Mounting of the field lenses within the objective requires a first precise mount, another mount is necessary for securing the field lens system within the objective housing. This multi-mounting method involves centering errors which in turn cause coma and astigmatism.

SUMMARY OF THE PRESENT INVENTION

The principal object of this invention is to provide a high speed compact catadioptric objective system of simple construction and high image quality with improved performance with respect to the above mentioned deficiencies.

The optical system of this invention comprises, in accordance with the advance of the light rays, a positive lens with a convex surface toward the object, a solid lens with front and back surface concave toward the object and with a main mirror lens constituted by the peripheral portion of said solid lens, a counter-mirror surfaced to the central portion of said positive lens and a field lens cemented to the central portion of said lens with the main mirror surfaced on the peripheral portion thereof. This catadioptric system comprises only two optical members which carry said mirrors and of which at least one member carries an additional lens element.

The present invention will be described more in detail with reference to illustrative embodiments shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a first embodiment of the present invention;

FIG. 2 shows a cross sectional view of a further embodiment of this invention;

FIG. 3 shows a cross section of a third embodiment of this invention;

FIG. 4 illustrates a cross section of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments shown in FIGS. 1 through 4 have only two optical members. As disclosed in FIG. 1 and FIG. 2 a front lens L₁ is surfaced with a counter-mirror M₂ on the central portion of its back surface facing the image side of the lens system. A main mirror lens M₁ is constituted by the outer portion of a solid lens L₄, the reflecting back surface of which faces the image side. This lens L₄ has no center bore and a field lens L₂ as shown in FIG. 1 or L₂, L₃ as shown in FIG. 2 is cemented to the central portion of lens L₄ facing the object side.

In FIG. 3 is shown a third embodiment of the invention likewise comprising a front lens L₁, a solid lens L₄ and a field lens L₂ cemented to the central portion of lens L₄. The counter-mirror M₂ now is surfaced on the central portion of the front surface of the front lens L₁ facing the object side, and an additional lens element L₅ is cemented on the central portion of the back surface of lens L₁ facing the image side.

The objective system illustrated in FIG. 4 also includes a front lens L₁, a solid lens L₄ and a field lens L₂ cemented to the central portion of lens L₄. A lens element L₅ with the counter mirror M₂ surfaced on its back-object side is cemented to the central portion of the surface of front lens L₁ facing the image side.

According to the above described construction a high speed catadioptric objective system lens is obtained, the image quality of which features a very reduced sensitivity to centering errors. The examples shown are highly corrected with respect to spherical and chromatic aberration, coma and astigmatism. They allow a compact construction and render superfluous a separate mechanical mount for the field lens system. An economical production and a reduced sensitivity to machining and mounting errors are brought about by the invention as it employs only two optical members for the objective.

The examples 1, 2, 3 and 4 of embodiments described above with reference to FIGS. 1, 2, 3 and 4 are shown in the following tables, where F is the aperture or speed of the lens system, f is the focal length and s' is the back focal distance.

EXAMPLE 1

    ______________________________________                                         F = 1:1.2      Thicknesses                                                     f = 99.7       and                                                             s' = 8.7       Separations n.sub.d ν.sub.d                                  ______________________________________                                         L.sub.1                                                                               r1 = +747.831                                                                              d1 = 7.5    1.76180                                                                              27.0                                             r2 = -2214.349                                                                             a2 = 46.9                                                   M.sub.1                                                                               r3 = -137.033                                                                              d3 = 8      1.68900                                                                              49.4                                             r4 = -198.791                                                                              d4 = d3                                                            r5 = r3     a5 = a2                                                     M.sub.2                                                                               r6 = r2     a6 = 41.9                                                   L.sub.2                                                                               r7 = +37.388                                                                               d7 = 5      1.46450                                                                              65.8                                             r8 = r3     d8 = d3                                                     L4     r8 = r3     d8 = d3     1.68900                                                                              49.4                                             r9 = r4                                                                 ______________________________________                                    

EXAMPLE 2

    ______________________________________                                         F = 1:1.2      Thicknesses                                                     f = 99.5       and                                                             s' = 9.0       Separations n.sub.d ν.sub.d                                  ______________________________________                                         L.sub.1                                                                               r1 = +639.795                                                                              d1 = 7.5    1.74000                                                                              28.2                                             r2 = -2444.988                                                                             d2 = 47.1                                                   M.sub.1                                                                               r3 = -138.122                                                                              d3 = 8      1.68900                                                                              49.4                                             r4 = -201.857                                                                              d4 = 18                                                            r5 = r3     a5 = 12                                                     M.sub.2                                                                               r6 = r2     a6 = 89.7                                                   L.sub.3                                                                               r7 = +37.94 d7 = 0.5    1.59551                                                                              39.2                                             r8 = +29.527                                                                               d8 = 4.9                                                    L.sub.2                                                                               r8 = +29.527                                                                               d8 = 4.9    1.46450                                                                              65.8                                             r9 = r3     d9 = d3                                                     L.sub.4                                                                               r9 = r3     d9 = d3     1.68900                                                                              49.4                                             r10 = r4                                                                ______________________________________                                    

EXAMPLE 3

    ______________________________________                                         F = 1:1.2      Thicknesses                                                     f = 99.4       and                                                             s' = 7.6       Separations n.sub.d ν.sub.d                                  ______________________________________                                         L.sub.1                                                                               r1 = +343.171                                                                              d1 = 7.5    1.51454                                                                              54.7                                             r2 = -590.667                                                                              a2 = 53.7                                                   M.sub.1                                                                               r3 = -267.451                                                                              d3 = 8      1.51680                                                                              64.2                                             r4 = -420.875                                                                              d4 = d3                                                            r5 = r3     a5 = 48.9                                                   L.sub.5                                                                               r6 = +212.359                                                                              d6 = 4.8    1.58215                                                                              42.1                                             r7 = r2     d7 = d1                                                     M.sub.2                                                                               r8 = r1     d8 = d1                                                     L.sub.5                                                                               r9 = r2     d9 = d6     1.58215                                                                              42.1                                             r10 = r6    a10 = 40.9                                                  L.sub.2                                                                               r11 = +35.652                                                                              d11 = 8     1.56883                                                                              56.1                                             r12 = r3    d12 = d3                                                    L.sub.4                                                                               r12 = r3    d12 = d3    1.51680                                                                              64.2                                             r13 = r4                                                                ______________________________________                                    

EXAMPLE 4

    ______________________________________                                         F = 1:1.2      Thicknesses                                                     f = 99.3       and                                                             s' = 10.0      Separations n.sub.d ν.sub.d                                  ______________________________________                                         L.sub.1                                                                               r1 = +174.38                                                                               d1 = 7.5    1.54041                                                                              51.1                                             r2 = +1165.501                                                                             a2 = 46.7                                                   M.sub.1                                                                               r3 = -205.617                                                                              d3 = 8      1.62004                                                                              36.4                                             r4 = -280.458                                                                              d4 = d3                                                            r5 = r3     a5 = 42.5                                                   L.sub.5                                                                               r6 = +369.399                                                                              d6 = 4.3    1.62237                                                                              36.0                                             r7 = r2     d7 = d6                                                     M.sub.2                                                                               r7 = r2     d7 = d6                                                     L.sub.5                                                                               r8 = r6     a8 = 32.4   1.62237                                                                              36.0                                      L.sub.2                                                                               r9 = +37.489                                                                               d9 = d10    1.4650                                                                               65.8                                             r10 = r3    d10 = d3                                                    L.sub.4                                                                               r10 = r3    d10 = d3    1.62004                                                                              36.4                                             r11 = r4                                                                ______________________________________                                          It will be appreciated that various modifications and changes of the      preferred embodiments described above may be made without leaving the      scope of the invention as defined in the accompanying claims. 

I claim:
 1. A high speed catadioptric objective system lens consisting of:a positive front lens with the front surface radius being smaller than the rear surface radius; a negative meniscus lens on the image side of said positive front lens with the back surface being convex toward the image and provided with a mirrored portion surrounding a light permeable central portion; a positive lens cemented onto the front surface central portion of said negative meniscus lens; and a counter mirror applied to the central portion of said positive front lens.
 2. A high speed catadioptric objective system lens consisting of:a positive front lens with the front surface radius being smaller than the rear surface radius; a negative meniscus lens on the image side of said positive front lens with the back surface being convex toward the image and provided with a mirrored portion surrounding a light permeable central portion; a positive cemented pair cemented onto the front surface central portion of said negative meniscus lens; and a counter mirror applied to the central portion of said positive front lens.
 3. A catadioptric system lens according to claim 1 or 2 wherein the rear surface of said positive front lens is convex toward the image, said counter mirror being applied to the central portion of said rear surface.
 4. A high speed catadioptric objective system lens consisting of:a positive front lens with the front surface radius being smaller than the rear surface radius; a negative meniscus lens on the image side of said positive front lens with the back surface being convex toward the image and provided with a mirrored portion surrounding a light permeable central portion; a positive lens cemented onto the front surface central portion of said negative meniscus lens; a counter mirror surfaced to the front surface central portion of said positive front lens; and a negative lens cemented onto the back surface central portion of said positive front lens.
 5. A high speed catadioptric objective lens consisting of:a positive front lens with the front surface radius being smaller than the rear surface radius; a negative meniscus lens on the image side of said positive front lens with the back surface being convex toward the image and provided with a mirrored portion surrounding a light permeable central portion; a positive lens cemented onto the front surface central portion of said negative meniscus lens; and a negative lens with a counter mirror silvered onto its object side surface, the negative lens cemented onto the central portion of the central portion of the surface toward the image of said positive front lens. 